# CVE-2026-100639: SiYuan before v3.8.4 Cross-Site Scripting via Kramdown IAL

> An attacker can achieve remote code execution by tricking a victim into pasting malicious Markdown that triggers XSS in the Electron desktop application.

- **Severity:** High 8.6 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 26 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-2cmm-9x9j-rvff, GHSA-r9x8-34vf-7m8q

## What is CVE-2026-100639?

CVE-2026-100639 is a high-severity cross-site scripting vulnerability in siyuan-note siyuan, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

SiYuan v3.8.3 fails to HTML-escape the data-subtype attribute when generating gutter-button markup (app/src/protyle/gutter/button.ts, assigned via innerHTML in app/src/protyle/gutter/index.ts) from content pasted as plain-text Markdown containing a Kramdown inline attribute list (IAL). Because the shared Lute renderer parses Kramdown IAL from text/plain input, an attacker-supplied Markdown snippet using entity-encoded quotes in data-subtype breaks out of the attribute value when the gutter markup is re-parsed by the browser, injecting additional attributes such as autofocus and onfocus. If a victim pastes the crafted Markdown and the affected gutter control receives focus, the injected handler executes; in the Electron desktop application, where the main BrowserWindow enables Node integration and disables context isolation, this results in JavaScript execution with renderer Node.js privileges (remote code execution). Fixed in v3.8.4.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-100639?


## How do I fix CVE-2026-100639?

No fix has been published for CVE-2026-100639 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100639 being exploited?

There is no known exploitation of CVE-2026-100639 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100639 and fix it if it is affected.

What it is: CVE-2026-100639 is a high-severity cross-site scripting vulnerability in siyuan-note siyuan, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-100639 in the wild and no public exploit code.

Affected product: siyuan-note siyuan. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-100639/ (Markdown: https://insights.sbomify.com/CVE-2026-100639/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100639
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100639
- OSV: https://osv.dev/vulnerability/CVE-2026-100639

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-100639/
Summaries are generated and may contain mistakes; the official description above is the record.